The invention relates to a differential mechanism with double gear ratio transmission for vehicles, in particular for heavy-duty power machines with adjustable wheel tracks, such as farm machinery, in which a combined main drive is used, which is provided with a central wet disc brake construction and a connectable gear mechanism with restricted slip. Epicyclic gear mechanisms are arranged in the main gear housing to have an improved self-aligning ability, while the driving axles are arranged with improved bearing locations.
Running gears used in power machines with adjustable wheel tracks (also known as rod-type running gears) have to meet the most complicated--and frequently contradictory--requirements. For example, wide wheel tracks require solid half-shafts carried by perfectly adjusted bearing supports with high loadability; narrow wheel tracks require a middle-part with the minimum space requirement, which influences negatively realization of proper conditions related to the wide wheel tracks.
In vehicles lacking wheel hub drives, brake constructions can be arranged in main gear housings only. These are the so-called internal or wet-brakes. However, these solutions influence negatively the realization of the narrow and wide wheel track as well, as in this case the width of the middle-part is increased and, simultaneously, the space serving for the bearing supports of the drive shafts will be reduced.
Running gears of heavy-duty power machines with adjustable wheel tracks are designed generally with double gear transmissions based largely on conceptions that enable the width of the middle-part of the running gear to be reduced. This involves, however, the application of epicyclic gears with a high reduction ratio (generally over 5) and a bevel gear-crown-wheel pair also with a high gear ratio. The wide bearing basis required for a stiff bearing to support a crown wheel of a large diameter also exerts a negative influence on the possible realization of narrow and wide wheel tracks respectively.
When using wide wheel tracks, wheel forces are transmitted through large arms via the half-shafts to the gear housings and the middle-part of the running gear. When these half-shafts are stiffly assembled and not arranged as so-called "floating" half-shafts, they require most careful assembly. Otherwise, their useful life will be very short due to the considerable deformation of elements of the drive-chain.
Modern types of running gears used in agricultural power machines require differential mechanisms with restricted slip, with the possibility of coupling and decoupling the limited slip mechanism. Taking into consideration that, with the rod-type gears, "everything" is arranged in the middle-part and "everything" performs a rotary motion, a coupling fork cannot be built in. This is particularly true if the running gear is to be provided with an internal brake construction. For this reason, mechanically actuated differential gears with restricted slip--considered as the most reliable construction--have never been used.
The requirements mentioned above are met by the known construction only functionally. That means that they are reliable and able to function. However, contradictory characteristics are not eliminated. In other words, new constructional solutions are not paired with these running gears in order to fulfill tasks different from the traditional ones. By choosing obvious and offered solutions, the users accept the fact that parameters of the running gears are such as can be obtained with the traditional solutions. From this it results that generally known running gears for adjustable wheel track equipment (John-Deere, Massey-Ferguson, Steyr, etc.) are based on nearly identical principles of design, and they differ only in respect to partial solutions of the construction. These basic principles can be summarized as follows:
The differential gear driven with a bevel gear/crown wheel pair is generally supported by bearings in an "X"-arrangement. After the differential gear, the sun wheels --forming a monolithic unit with inner half-shafts--drive epicyclic gears, which are arranged adjacent the sides of the middle-part of the main housing. The carriers of the epicyclic gears are provided with an internal rib to drive directly the external axles.
One unit each of the generally hydraulically actuated inner disc brakes--one for each side--is arranged between the middle-part of the main housing and the epicyclic gears so that the active rotating discs engage with the teeth of the sun wheel.
A solution is also known, with which the rotating braking discs engage the carrier of the epicyclic gear, that being the drive element with the largest moment.
In the housing of the differential gear, formed with one or more dividing planes, differential gears with main drive pinion are used. Restricted slip is achieved in such manner that the traditional differential gear includes a hydraulically actuated or spring-pre-stressed bundle of lamellae, or the increased internal friction is established proportionally with the moment of the differential gear, e.g., by inserting a disc with spur-gearing with a large contact angle.
Now let us survey the negative features resulting from the described and presently used basic principles of projecting:
(1) Uniform support of the crown-wheel differential gear housing by bearings in an "X"-arrangement enables simple adjustment of the backlash and the bearings of the equalizing gear by means of the generally known bearing nuts. At the same time, in practice, a cross-spread arrangement (in other words, an "O"-arrangement) would result in a far more effective bearing basis.
(2) The disc brake, arranged on one side of the bridge housing has a considerable space requirement. If the users demand an external transmission brake instead of the internal wet-brake, the remaining unutilized empty space influences negatively the parameters of the running gear. This results from the fact that it is not at all economical to design separate constructions for both external and internal braking systems, as the number of produced running gears of either type is relatively low.
(3) In known constructions, active discs of the disc brake usually engaged with teeth of the sun-gear (side gear) or with the ribs on internal self-adjusting (so-called "floating") half-shafts. This is a rather contradictory solution, desirably affecting both the brake and the epicyclic gear, because the rotating brake discs, loaded with moment and requiring a good driving connection, are engaged with the side gears requiring, which must have the ability of self-adjustment, or with the inner half-shafts.
(4) Supporting bearings of the crown-wheel in an "X"-arrangement, as well as arranging the brake units along side of the middle-part of the main housing, practically excludes the possibility that a mechanically actuated differential gear with a selectively engageable restricted slip could be used. Hydraulically actuated lamella-bundles are more expensive and less reliable. At the same time, lamella-bundles which are are constantly pre-stressed with spring force, and which cannot be uncoupled, exert a negative influence on the driving system and abrade the tires, if the power machine travels on good surfaces, e.g., on a concrete road. Differential gears mechanisms where the coefficient of friction is increased proportionally with the moment (e.g., differential gears, incorporating discs with spur-gears with a large connection angle and combined with a bundle of lamellae) are efficient generally only if the desired high moment is available.
(5) With crown-wheel-differential gear supported in bearings with an "X"-arrangement, the differential gear housing is laterally closed. Accordingly, to obtain lamella-bundles with proper energy absorption, i.e., of sufficient volume--more than one dividing plane must be provided in the differential gear housing, involving compellingly increased costs.
(6) Bar-axles of running gears with adjustable wheel tracks are rigidly assembled. Bearing support is provided by bearings with high loadability adjusted to be tight fitting. Driving bar-axles are driven directly from the carriers of the epicyclic gears, through a ribbed drive. In practice, this drive is realized so that the ribbed hub of the carrier of the epicyclic gears is clamped rigidly between an inner taper-roller bearing of the bar-axle and a so-called supporting plate, as the hub of the carrier of the epicyclic gear also partakes in the support. Due to the rigid clamping of said carrier, self-adjusting ability of the gears is restricted. As a consequence, the gears receive accessory loads, as deformations of the loaded bar-axles are transferred to the epicyclic gears, thus shortening their useful life. That means that there is a disturbing interaction between the epicyclic gears and the bearings of the bar-axles.
The invention is based on the development of a heavy-duty running gear with internal disc brakes and a differential gear with restricted slip which can be mechanically coupled and uncoupled with restricted dimensions of the middle-part in consideration of the requirements of equipment with adjustable wheel tracks.
Power machines are known to which running gears with constant wheel tracks are used and with which epicyclic gear and brakes are arranged at the hub.
Power machines are also known which contain a central brake construction, which is mounted either on an auxiliary gear box or on the drive of the main drive of the--generally frontal--running gear. In both cases, it is important that the vehicle should meet all the requirements in respect to safe braking. It is quite obvious that the conventional solution for running gears with adjustable wheel tracks, wherein separate wet-brake constructions are arranged on each side, in other words for each wheel, results from the practice followed with traditional running gears, where wheel brakes used to be applied. The present invention is based on the recognition that one central so-called wet-brake suffices for running gears with adjustable wheel tracks, if this wet-brake is incorporated as part of the running gear.
In the middle-part of the running gears with adjustable wheel tracks, next to the driving bevel gear--on the side lying opposite to the crown-wheel--there is an expedient space for installing a centralized brake construction. If the centralized brake is arranged here, widening of the middle-part of the running gear becomes superfluous, as space requirements of the side facing the crown-wheel will be determinant in this case. In running gears designed in compliance with generally known practice, due to the symmetry related to the longitudinal axis of the vehicle (e.g., generally the two sides of the main housing are completely identical), the side facing the crown-wheel is not at all utilized. By the central arrangement according to the invention the housing of the equalizing gear is part of the brake construction; active brake discs are connected with the housing of the equalizing gear.
In order to be able to realize controllable, mechanical coupling of the differential gear with restricted slip, the housing of the equalizing gear must be accessible from the end. This could be achieved by placing the brake construction around the equalizing gear. A further prerequisite of accessibility is that the housing of the equalizing gear should be open on the end. This requirement can be met if the unit consisting of the equalizing gear and the crown-wheel is supported in bearings in a "cross-spread" arrangement, and in this way, further accessory advantages can be obtained. First of all, compared to the "X"-arrangement, the "cross-spread" arrangement of the bearings guarantees--with the same space requirement--a far better bearing basis. On the other hand, it enables the bundles of lamellae to be of sufficient volume, i.e., having the required ability of energy absorption to be installed from the outside. Further advantages are that the housing of the equalizing gear does not require more than one dividing plane. Moreover, the bundle of lamellae providing restricted slip, which completes the traditional differential gear with bevel gears, can be simply omitted, where desired, without disassembling the differential gear.
Adjacent the end of the middle-part of the running gear lying opposite to the crown-wheel--we established the conditions for installing a coupling fork. Thus, we produced a combined main drive unit provided with a centralized brake construction and with a differential gear with restricted slip with the possibility of controlled coupling.
The centralized braking system according to the invention--in contrast to general practice--does not brake the sun wheel (which requires the ability of self-adjustment) or the inner half-shafts, but it is connected to the housing of the equalizing gear. The latter is supported in bearings and provides an excellent guide to the rotating brake discs. In such a manner, the self-adjusting ability of the epicyclic gears can be improved.
The other part of the task to be solved is to make the epicyclic gears independent of the effect of the loaded half-shafts. As already mentioned before, according to presently known general practice, the hub-part of the carrier of the epicyclic gear, being clamped rigidly between the inner taper-roller bearing of a bar-axle and the supporting plate, transfers the driving moment to said bar-axles with the aid of ribs. Deformations of the loaded bar-axles are transferred to the carriers of the epicyclic gears and produce external loads in the epicyclic gear elements, which are restricted in respect to self-adjusting ability. This results in a shortened useful life.
In accordance with the invention independence of the epicyclic gears is realized so that a bushing--provided with ribs on both the outside and inside--is inserted between the bar-axle and the hub-parts of the epicyclic gear carriers. This bushing is clamped rigidly between an inner taper-roller bearing of the bar-axle and a supporting disc fitted tightly on the bar-rod by means of the ribs, while the hub-part of the carrier of the epicyclic gear is fitted loosely to the outer ribs. However, this hub-part does not partake in supporting the bearing of the bar-axle. In such a manner, the carrier of the epicyclic gear becomes completely self-aligning and independent: by the aid of the ribbed bushing it continues to transfer the driving moment to the bar-axle, but it is relieved from the deformations.
It is considered as essential that the loose rib bond be arranged outside the plane of the epicyclic gear. In such a manner, not only angle-setting but also compensation of errors resulting from eccentricity become possible. Application of the ribbed bushing yields the possibility that adjustment of the bearings of the bar-axles can be performed without affecting the carriers of the epicyclic gear, as only the bushing is involved in sustaining the bearings.
Application of the bushing according to the invention facilitates servicing of the running gears, as in the course of repairing or exchanging the epicyclic gears, bearings of the bar-axles need not be disassembled, which would be unavoidable with the presently known constructions.
Accordingly, we succeeded to realize another most important aim: epicyclic gears can be rendered completely independent and self-aligning. They are not influenced either by the brake constructions or the bar-axles, resulting obviously in the considerable prolongation of the useful life of the force transmitting elements without the necessity of increasing the dimensions or using special material quality or technologies.